An overvoltage protection device comprises a protective element which is, as a rule, represented by a nonlinear resistor element (varistor) which gradually decreases its resistance value due to applying electric current and pulse loading to the protected mains. In consequence, the current flowing through the protective member increases, and the temperature of the protective member rises. Thus the overvoltage protection is further fitted with a temperature shutdown device. This serves to disconnect the protective member from the mains in the case of reaching a particular temperature of the protective member, because the protective member is not any further able to carry out the function properly due to its temperature rise. Disconnecting the protective member from the mains is indicated either visually directly on the overvoltage protection device or by means of a remote indication. When the protective member is disconnected from the mains, the mains is no longer protected, so it is necessary to renew the status of protection by replacing the overvoltage protection protective member.
The overvoltage protection device generally comprises a U-shaped bracket mounted in a supporting device, and conductors of a protected circuit are connected to the overvoltage protection device, simplifying replacement of the protective element. The overvoltage protection device further comprises a slide-in protective member fitted with contacts for connecting to a current path arranged in the bracket and connected to the protected mains whereas the slide-in protective member is slid into the bracket. Thus, the slide-in protective member is easily replaceable and includes a nonlinear resistor element, a thermal device to disconnect the nonlinear resistor element, a device for visual indication of the status of the overvoltage protection device, and possibly also suitable devices for detecting the status of the overvoltage protection device to remotely indicate the change of the overvoltage protection.
There are many embodiments known, whereas their particular arrangement and used components depend on energy load and impulse current amplitude which passes through the current path of the overvoltage protection. Nowadays used embodiments depend also on manufacturing technologies used at the production of slide-in protective members. Changes in design of slide-in protective members then follow the basic goal of lowering the manufacturing costs with concurrent maintenance of required properties of overvoltage protections.
A well-known device according to Utility Design DE 295 19 313 U1 as a shutdown device of the nonlinear resistor element uses a shaped copper strip which is on one side firmly connected to a contact of the slide-in protective member and on the other side it is connected to a varistor electrode by means of thermally suitable solder. There is a hinged lever acting against the shaped copper strip, where the pressure towards the shaped copper strip is provided by means of a pressure spring which is arranged between the hinged lever and fixed (immobile) shackle of the other end of the spring. The hinged lever serves both for visual indication of the overvoltage protection status change (disconnecting the varistor from the mains) and also for acquiring the information on the status change for the remote indication.
The drawback of this solution is in that it does not allow placing varistors connected in parallel or varistors of bigger sizes, for example, into the bushing of the slide-in protective member due to its space arrangement, which limits variability of the protective properties of this solution while maintaining the outer dimensions of the slide-in protective elements. Another drawback of this solution is the use of a sealing compound for insulation and fixation the varistor in the bushing of the slide-in protective member, which increases the costs.
Another known device according to EP 436 881 A1 utilizes the disconnecting element arrangement perpendicularly to the plane of the varistor. The disconnecting component is a copper strip which is on one side mounted to the contact of the slide-in protective member, and it is connected on the other side to the outlet of the varistor electrode by means of thermally suitable solder. The disconnecting element is arch-shaped, and there is a hole in its centre, into which a hinged lever reaches. The hinged lever forms the necessary action on the disconnecting element by means of the pressure spring, and the disconnecting element, after the solder is melted, moves to the position in which the disconnecting of the varistor from the mains is ensured.
The drawback of this solution is the use of relatively rigid disconnecting element that requires considerable force to deform and which sets decent demands on dimensioning in the system of used components and thus also the solution cost. Another drawback of the solution is the space arrangement of the solution which takes the inner space of the slide-in protective member body up whereas the space can be potentially used for next varistors or for another size of a varistor.
Another known device as a disconnecting element uses a copper strip which is on one of its end connected with the varistor electrode by means of thermally suitable solder. A copper cable connected to its other end is connected to the contact of the sliding member whereas there is a hinged lever reaching into the opening of the disconnecting element. The hinged lever reduces the force against the disconnecting element by means of the pressure spring.
The advantage of this solution is that the copper cable represents a flexible component which needs only a small force to deform, but the drawback of the solution is the increase of the number of components on the current path. This increases the number of connections which are needed to be formed during manufacturing and thus the manufacturing costs are increased.
The goal of the invention is to eliminate or at least to minimize the drawbacks of the today's background art.